German Patent No. 195 34 445 describes a fuel injector which has an actuator arranged in an actuator chamber and a valve-closure member which can be actuated by the actuator via a valve needle, the valve-closure member cooperating with a valve-seat face to form a sealing seat. The valve needle is joined positively to a pressure shoulder via which the actuator acts upon the valve needle against the force of a compression spring. In this context, the pressure shoulder and the valve needle are guided in a valve housing. To direct the fuel in the direction of the sealing seat, the pressure shoulder and the valve needle each have one central bore. To seal the actuator against the fuel, the guideway between the pressure shoulder and the valve body or between the valve needle and the valve body has a sealing design. Since the valve needle and the pressure shoulder, respectively, must be able to move in the valve body, the actuator is not completely sealed against the fuel but only against the fuel pressure.
The fuel injector described in German Patent No. 195 34 445 has the disadvantage that the actuator continues to be subjected to the chemical action of the fuel, and that the mobility of the valve needle is deteriorated by the seal. Besides, the service life of the fuel injector is reduced by the arising friction.
German Patent No. 42 32 225 describes a device, where a piezoelectric actuator is sealed against a pressurizing medium. In this context, the seal is effected via an elastic sealing element. In this connection, the pressurizing medium is used for transferring the lift, and is therefore not charged with a high pressure. However, the seal described in German Patent No. 42 32 225 is not suitable for fuels, particularly not for fuel under very high pressure. In the case of fuel under very high pressure, the problem arises that the connection between the sealing element and a body (housing) does not withstand the high fuel pressure. Besides, fuel has a high permeation so that the sealing elements are penetrated by the fuel, as a result of which fuel or fuel-vapor gets through the seal. This applies particularly to gasoline fuel.
The fuel injector according to the present invention has the advantage that a permeation-resistant sealing of the actuator is achieved. In this manner, the actuator is protected both from the pressure of the fuel and from the chemical action of the fuel.
Advantageously formed between the two elastomer seals is a space which is vented by a vent duct. In this manner, fuel gas penetrating through the first elastomer seal is led out of the space so that the sealing of the actuator against the fuel is further improved.
The fuel injector expediently has an axially movable actuator housing having a pot-shaped design, the housing at least partially surrounding the actuator, and being surrounded at least sectionally by the elastomer seals. Thus, a lift of the actuator is made possible in a simple manner.
During a lift of the actuator, the elastomer seals are elastically deformed without sliding motion so that no friction losses result, which improves the long-term stability of the fuel injector.